The recent introduction of acetylene-terminated polyimides to produce cured reaction products which are stable at very high temperatures of 450.degree. C. and up has created an interest and need to produce the polyimides at attractive and competitive costs. The prime difficulty in the preparation of the acetylene-terminated polimides which are described, for example, in U.S. Pat. No. 3,845,018 and U.S. Pat. No. 3,879,349, both to Norman Bilow et al, is the preparation of the monomers which include in one instance the preparation of meta-aminophenylacetylene (APA). This invention relates to the discovery of an unsupported ruthenium disulfide catalyst which selectively converts at high conversion levels the nitroaromatic acetylene compounds used in the process of this invention, e.g., nitrophenylacetylene, to the desired APA, provided the charge stock nitroaromatic acetylene is contacted with the catalyst in a dilute concentration in an inert solvent. By a "dilute concentration" is meant a concentration of less than about six weight percent. By following the teachings of this invention, high conversions of over 50 weight percent of the nitroaromatic acetylene are achieved, together with very high selectively of well over 70%, typically well over 90%.